218 ME. W. P PYCRAFT ON THE MOEPHOLOGT AND 



The sternum of Dromceus ater is remarkable, possessing as it does cliaracters in 

 common with both Casuarivs and Rhea, but is at the same time Dromseine. 



As in I), noire-hollandice, the anterior lateral processes are conspicuously largo and 

 have the same form. The outline of the free edge of the corpus sterni from the 

 articulation of the last thoracic rib backwards is the same. The coracoid grooves 

 are obsolete. That of the right side is represented by a portion (jf the inner angle of 

 the lower lip of the groove. This, as is seen in the figure (4 b), persists in the form 

 of a median asymmetrical tubercle. The obsolescence of these grooves indicates that 

 the pectoral arch and wing were much more degenerate than in Dromceus novrt^- 

 hollandiw or I), irroratus. The corpus sterni differs from that of D. novw-liollandke in 

 the relatively much greater development of the protuberantia sterni, which resembles 

 that of Bhea, and in the relatively narrower width across the region of the incipient 

 posterior lateral processes. Four ribs articulate with the sternum, in D. novce- 

 hoUandia' only three. 



The following measurements in millimetres are of interest : — 



B. novce-Jiollandice. D. ater. 



Greatest lengtli 160 95 



Greatest width (across aut. lat. proc.) . . 1 10 90 



Least width (across post. lat. proc.) ... 105 55 



It should be noted that the metasternum of J), ater bears traces of fracture, 

 indicating a somewhat greater length than the above measurements. The breadth of 

 the sternum nearly equals its length. In Casuarius it is much longer than broad. 

 The articular surfaces for the sternal ribs are divided one from another by pneumatic 

 apertures forming pockets of great depth, extending from Avithout inwards towards 

 the middle line. The hinder border, both in Dromcpus and Casuarius, is shield-shaped. 

 No external lateral processes are present. The sternal plate is of great thickness and 

 highly pneumatic. 



In the young Dromceus the anterior lateral processes are very short, and the ventral 

 margins of the coracoid grooves are almost confluent and not separated by a deep 

 median notch. 



In Casuarius the sternum is relatively much longer than in Dromceus, the increase in 

 length being most noticeable from the articulation for the last thoracic rib backwards. 

 The coracoid grooves are much longer, and the anterior lateral process is almost 

 obsolete. In the middle line between the ventral lips of the coracoid groove in 

 Casuarius there opens forward a large pneumatic aperture ; this runs backwards into 

 the body of the bone for some considerable distance, penetrating a low median ridge 

 or protuberance resembling a vestigial keel. This is wanting in C. unappendiculatuSf 

 a shallow groove taking its place, the sides of which further back become conspicuously 

 raised to form a pair of long low ridges. 



